Oriented polymer hinge pins in modular plastic conveyor belts

ABSTRACT

A modular plastic conveyor belt hingedly interconnected by hinge pins made of a highly oriented polymer material. The hinge pins are preferably extruded from a material including a highly oriented polymer, such as polyethylene, polypropylene, or nylon. Alternative materials include highly oriented acetal or polyurethane. Plastic hinge pins made with these polymers having their long molecules oriented along the axis of the shaft of the hinge pin are exceptionally strong and resistant to deformation.

BACKGROUND

[0001] The invention relates to modular plastic conveyor belts and, moreparticularly, to hinge pins for connecting consecutive modular belt rowstogether, wherein the hinge pins are made of an oriented polymermaterial.

[0002] Because they do not corrode and are easy to maintain, modularplastic conveyor belts are widely used in many industries to conveyarticles. These belts, or chains, are typically constructed of a seriesof rows of one or more belt modules connected end to end into an endlessconveyor belt. Each row includes spaced apart hinge elements at each endwith apertures formed through them. The hinge elements along one end ofa row are interleaved with the hinge elements along an end of anadjacent row. The apertures of the interleaved hinge elements arealigned and form a passageway. A hinge pin inserted in the passagewayserves to connect the rows together and to allow them to pivot about theaxis of the pin so that the belt can backflex or articulate about adrive sprocket. Hinge pins are typically molded or extruded of athermoplastic material, such as polypropylene, polyethylene, nylon,acetal, or composite polymers.

[0003] As the belt moves, belt tension is borne not only by the modulesbut also by the hinge pins. Each row of belt modules pulls the trailingrows. This belt pull, or tension, is transmitted row to row through thehinge pins. With each row of interleaved hinge elements pulling inopposite directions, the hinge pin can, over time, deform, assuming acorrugated, or stepped, shape resembling a cam shaft. Cam-shafting ofhinge pins causes problems.

[0004] One problem caused by cam-shafted hinge pins is scrubbing of thehinge pin against the walls of the apertures in the hinge elements.Because a cam-shafted hinge pin has a preferred orientation relative toits confining hinge elements, scrubbing and the consequent wear areconcentrated on the same portions of the hinge pin's outer surface. Thistends to accelerate the wear of the hinge pin.

[0005] A second problem caused by cam-shafted hinge pins is elongationof the belt. A cam-shafted hinge pin connecting two adjacent rows ofbelt modules allows the apertures of one row to move out of alignmentwith those of the adjacent row, effectively lengthening the pitch of therow and stretching the belt's overall length. Wallowing out of theapertures by scrubbing against the hinge pin adds to the belt-stretchingproblem. The increased length means more sag in the belt on thereturnway, for which space must be allocated. The longer pitch of thebelt can adversely affect engagement of the belt with fixed-pitch driveand idler sprockets. Poor sprocket engagement makes for a less uniformconveying speed and a bumpier ride. Accelerated wear of, and even damageto, the belt drive surfaces and the sprockets are other results of poorsprocket engagement. Conditions such as heavy loading and hightemperatures can exacerbate these problems caused by cam-shafted hingepins.

[0006] One way these problems have been addressed is through the use oflarger diameter hinge pins for increased strength and lesssusceptibility to deformation. Another approach is to change thegeometry of the modules to compensate for weak hinge pins. But theseapproaches often represent compromises that adversely affect otherperformance characteristics. For example, larger hinge pins requirelarger hinge-element apertures, which means that, with more materialremoved, the hinge element is inherently weaker.

[0007] Yet another approach is the use of stainless steel hinge pins,which are inherently stronger and stiffer and unlikely to deform as muchas conventional plastic hinge pins. But steel hinge pins are heavy. Theadded weight increases the tensile load on the belt modules and mayrequire larger drive motors. Furthermore, special pin retention schemesare often necessary to retain stainless steel hinge pins in belts.

[0008] Thus, there is a need for a modular plastic conveyor belt thatdoes not stretch over time, especially in heavy-load applications.

SUMMARY

[0009] These needs and others are satisfied by a modular plasticconveyor belt with a hinge pin embodying features of the invention. Thebelt is constructed of a series of rows of one or more belt modules.Each module extends from a first end to a second end in the direction ofbelt travel. A first set of hinge elements is arranged along the firstend of the modules in each row; a second set, along the second end. Thefirst set of hinge elements of a row interleaves with the second set ofhinge elements of an adjacent row. Aligned apertures formed in theinterleaved hinge elements define a passageway through the hingeelements. A hinge pin disposed in the passageway forms a hinge jointbetween adjacent rows. To prevent the belt from stretching, the hingepin includes a shaft made of a highly oriented polymer material forstrength. The material is preferably a highly oriented polypropylene,polyethylene, or nylon. As an alternative, the material could be ahighly oriented acetal or polyurethane. These polymers, with theirmolecules oriented along the length of the shaft, give the hinge pinhigh sheer strength and decrease its tendency to deform in a belt undertension.

DRAWINGS

[0010] These and other features, aspects, and advantages of theinvention are described in more detail in the following description,appended claims, and accompanying drawings, in which:

[0011]FIG. 1 is an isometric view of a portion of a modular plasticconveyor belt connected by hinge pins embodying features of theinvention; and

[0012]FIG. 2 is a partial top view of a prior art cam-shafted hinge pinin a conveyor belt shown cut away.

DETAILED DESCRIPTION

[0013] A portion of a modular conveyor belt connected by hinge pinsembodying features of the invention is shown in FIG. 1. The beltincludes a series of rows 10 of belt modules 12. Each belt moduleextends from a first end to a second end in a direction of belt travel14. Each module includes a first set of hinge elements 16 along thefirst end and a second set of hinge elements 17 along the second end.Each of the hinge elements has an aperture 18 formed therethrough. Theapertures of each set are aligned across the width of the module. Themodules are typically formed by injection-molding and made of athermoplastic material, such as polypropylene, polyethylene, acetal,nylon, or a composite material that may include non-plastic fibers forstrength. Belts made of such modules are manufactured and sold, forexample, by Intralox, Inc. of Harahan, La., USA.

[0014] The modular plastic conveyor belt is assembled by interleavingthe first set of hinge elements of a row with the second set of hingeelements of an adjacent row. Each row may include one or more modules.When multiple modules are used in each row, the modules are positionedside by side in the row and end to end with the modules of adjacent rowstypically in a brick-lay pattern and supported on wearstrips 19. Thealigned apertures of the interleaved hinge elements form a passagewaybetween each row across the width of the belt. The shafts of hinge pins20 are inserted into the passageways to interconnect the modules of onerow to those of an adjacent row and to form with the hinge elements ahinge joint between adjacent rows. The belt can articulate about a drivesprocket or drum at the hinge joints.

[0015] When the belt is driven, the modules and their hinge elements arein tension. The rows try to separate, but are held together by the hingepins. Over time, a conventional plastic hinge pin 20′ assumes acam-shaft shape as illustrated in FIG. 2. The apertures 18′, 18″ ofadjacent rows 10′, 10″ are offset out of coaxial alignment in accordancewith the amount of cam-shafting. Adjacent belt rows are separated, andthe entire belt is longer. Conventional plastic hinge pins, which aretypically extruded or molded of a thermoplastic such as polypropylene,polyethylene, acetal, or nylon, are especially susceptible tocam-shafting in heavy-load applications.

[0016] To avoid cam-shafting of hinge pins and the associated problems,strong hinge pins 20 made of an oriented polymer material are used tointerconnect belt rows into a conveyor belt as in FIG. 1. The hinge pinis preferably extruded according to the process described in U.S. Pat.No. 5,169,587, “Process for Extruding Large Oriented Polymer Shapes,”Gregory J. Courval, the disclosure of which is hereby incorporated byreference. A preferred group of polymers used in the highly orientedpolymer material include polypropylene, polyethylene, and nylon. Othermaterials that could be highly oriented include acetal and polyurethane.A hinge pin with its long polymer molecules oriented axially along therod exhibits high shear strength and resists deformation. A beltinterconnected with hinge pins made of these oriented polymers is lesslikely to stretch—even under heavy loading or at high temperatures.Because the hinge pin is made of plastic, the belt does not suffer theconsequences of using heavy stainless steel pins. Furthermore, the hingepin can be retained in the passageway using familiar headless rodretention schemes, or the hinge pin can be headed at one end andretained conventionally by snap-fit or obstruction.

[0017] Thus, a conveyor belt hingedly interconnected by strong hingepins made of a highly oriented polymer material avoids stretching andmaintains its pitch without a significant increase in weight.

[0018] It should be recognized that the strength advantages provided byoriented polymers could also be applied to plastic conveyor belt modulesand to conveyor accessories, such as flights, sideguards, hold downtabs, and sprockets, to name a few. Making these articles out of ahighly oriented polymer material could increase their lives in certainapplications.

[0019] The invention has been described in detail with respect topreferred versions, but the scope of the claims should not be limited tothe description of the preferred versions.

What is claimed is:
 1. A hinge pin for hingedly interconnecting adjacentrows of plastic belt modules through aligned apertures in interleavedhinge elements of adjacent rows, the hinge pin comprising: a shaft madeof a highly oriented polymer material.
 2. A hinge pin as in claim 1,wherein the highly oriented polymer is selected from the groupconsisting of polypropylene, polyethylene, and nylon.
 3. A hinge pin asin claim 1, wherein the highly oriented polymer is selected from thegroup consisting of acetal and polyurethane.
 4. A modular plasticconveyor belt comprising: a series of rows of belt modules wherein eachrow includes at least one belt module extending from a first end to asecond end in the direction of belt travel and including a first set ofhinge elements along the first end and a second set of hinge elementsalong the second end, wherein the hinge elements form aligned aperturestherethrough and wherein the rows are arranged end to end with the firstset of hinge elements of a row interleaved with the second set of hingeelements of an adjacent row, the aligned apertures of the interleavedhinge elements defining a passageway between adjacent rows; and a hingepin disposed in the passageway to form a hinge joint between adjacentrows, wherein the hinge pin includes a shaft made of a highly orientedpolymer material.
 5. A modular plastic conveyor belt as in claim 4,wherein the highly oriented polymer is selected from the groupconsisting of polypropylene, polyethylene, and nylon.
 6. A modularplastic conveyor belt as in claim 4 wherein the highly oriented polymeris selected from the group consisting of acetal and polyurethane.